This invention relates to a batch method for terminating solid electrolyte capacitors, and more particularly to such a method that produces a metal-loaded resin end-cap on both ends of a plurality of such capacitors.
Solid electrolyte chip capacitors having end-cap terminals are especially suitable for flush mounting to a printed wiring board, or the like, usually by reflow soldering thereto. An insulative protective layer is normally provided over a major portion of such a capacitor; which capacitor conventionally includes a porous valve-metal pellet having an oxide dielectric film formed over its surfaces, a solid electrolyte over the dielectric film, and a metallic counterelectrode over the solid electrolyte. A metal-loaded resin paint is applied over opposite ends of the pellet and partially over the insulative protective layer. One paint layer contacts the counterelectrode, and the other paint layer contacts a valve-metal riser wire extending from the pellet.
Batch fabrication of solid electrolyte capacitors is accomplished by suspending a plurality of pellets by their risers from a processing bar, and by positioning a plurality of such processing bars in a common carrier rack. The objective of batch fabrication of solid electrolyte capacitors is to accomplish as much as possible of the manufacturing cycle while the many pellets are in the common carrier rack. In other words the objective is to work on a full rack of capacitors (e.g. 3000) at each process step, rather than a single processing bar or even a single capacitor as taught in the prior art for one or more of the steps involved in terminating capacitors.
My prior U.S. Pat. No. 4,203,194 issued May 20, 1980 teaches the fabrication of solid electrolyte capacitors through to the production of end-caps on both ends of pellets while the pellets are welded to processing bars that are mounted in a common carrier rack. The end-caps are produced according to the parent application by spraying silver onto the top and bottom end faces of the pellets, and thereafter nickel plating the silver and then coating the nickel with solder.
The sprayed silver end-caps of my prior patent U.S. Pat. No. 4,203,194 are effective, but costly to produce because of the need for masking each pellet to ensure separation between the two end-caps. Part of the cost is the need to remove each processing bar from the carrier rack for the masking and spraying steps. This prior process also requires a large inventory of masks so as to accommodate the many sizes of capacitors that require end-caps. My prior end spray process is wasteful of silver, because much of the sprayed silver is deposited on the masks and surrounding equipment from which reclaiming is less than complete.